As widespread use of portable electronic products such as high quality smartphones, Pads and the like, requirements on earphones capable of cooperating with the electronic products are increasingly higher; the earphones are required to have a small size and hi-fidelity sound quality performances capable of realistically representing various sound effects. Furthermore, no matter what kind of the above-described electronic products are, in order to allow users to hear the sound signals provided by the electronic products without interfering with other people, the earphone has become an essential accessory for various electronic products. In addition, the earphone also provides a better sound transmission for the listener, so that the listener can clearly hear and understand the sound content.
The existing earphones can be divided into in-ear, on-ear and semi in-ear earphones according to wearing styles. The existing earphone mainly comprises a front housing of the earphone, a rear housing of the earphone and a loudspeaker unit (horn) accommodated within the front housing and the rear housing of the earphone. Since different earphone users have different requirements on the style of the earphone, furthermore it is also necessary to adjust the earphone into different frequency responses so as to adapt to the change of the environment for different application environments, therefore there is an urgent requiring for an earphone capable of voluntarily adjusting the frequency response of the earphone according to individual requirements so as to adapt to different users and application environments.